1. Field of the Invention
The present invention relates generally to analog-to-digital converting methods and apparatus, and more particularly to a method and receiver/decoder apparatus for converting standard "Touch-Tone" signals to digital signals which can be used in any of a large number of applications.
2. Description of the Prior Art
As the telephone industry changes over to the Touch-Tone dialing system, one of the problems which arises is the availability of apparatus capable of making full utilization of the signal transmission and handling benefits for which the Touch-Tone system was designed. Most prior art apparatus use analog techniques to perform the signal identification operations upon the analog signals received rather than converting such signals to digital form before decoding. As a consequence, such apparatus suffer disadvantages which make it impractical for portable applications. For example, presently available signal decoding apparatus operating in the analog domain are much too large in physical size and draw far too much electrical current to make them applicable for use in pocket-paging devices and other dial-signal responsive systems. Furthermore, such apparatus is expensive, relatively slow in operation and susceptible in jamming in ordinary use.
A related method and apparatus using digital techniques is disclosed in the U.S. Pat. No. 3,790,720 to Schartmann, entitled "Digital Decoder for Multiple Frequency Telephone Signalling."